Wood warping is a deviation from flatness as a result of stresses and shrinkage from the uneven drying of lumber.
The types of wood warping include:
bow : a warp along the length of the face of the wood
crook: a warp along the length of the edge of the wood
kink: a localized crook, often due to a knot
cup: a warp across the width of the face, in which the edges are higher or lower than the center of the wood
twist: a distortion in which the two ends do not lie on the same plane